Trigonometric Functions: 

double cos(double x); long double cosl(long double x); The cos() function calculates the cosine of a number. Consider AB the length of A to B, also referred to as the hypotenuse. Also consider AC the length of A to C which is the side adjacent to point A. The cosine of the angle at point A is the ratio AC/AB. That is, the ratio of the adjacent length, AC, over the length of the hypotenuse, AB: The returned value, the ratio, is a doubleprecision number between –1 and 1. 
Example: A form contains an Edit control named edtValue. After the user has typed a value and presses Enter, the OnKeyPress event retrieves the number typed in the edit box, calculates its cosine and displays it in the same Edit control: // void __fastcall TForm1::edtValueKeyPress(TObject *Sender, char &Key) { if( Key == VK_RETURN ) { double Value = edtValue>Text.ToDouble(); double Cosinus = cos(Value); edtValue>Text = Cosinus; } } //
double sin(double x); long double sinl(long double x); The sin() function calculates the sine of a number. Consider AB the length of A to B, also called the hypotenuse to point A. Also consider CB the length of C to B, which is the opposite side to point A. The sine represents the ratio of CB/AB; that is, the ratio of the opposite side, CB over the hypotenuse AB. The sin() function takes a doubleprecision number and returns one between –1 and 1. The sinl() function is used for 10byte values. Example: A form contains an Edit control named edtValue. After the user has typed a value and presses Enter, the OnKeyPress event retrieves the number typed in the edit box, calculates its sine and displays the result in the same Edit control: // void __fastcall TForm1::edtValueKeyPress(TObject *Sender, char &Key) { if( Key == VK_RETURN ) { double Value = edtValue>Text.ToDouble(); double Sinus = sin(Value); edtValue>Text = Sinus; } } //
double tan(double x); long double tanl(long double x);
The tan() function calculates the tangent of a number. Example: A form contains an Edit control named edtValue. After the user has typed a value and presses Enter, the OnKeyPress event retrieves the number typed in the edit box, calculates its tangent and displays the result in the same Edit control: // void __fastcall TForm1::edtValueKeyPress(TObject *Sender, char &Key) { if( Key == VK_RETURN ) { double Value = edtValue>Text.ToDouble(); double Tangent = tan(Value); edtValue>Text = Tangent; } } //
double atan(double x); The atan() function is used to calculate the arc tangent of a number.
The atan() function takes one argument, x, that represents the angle BA AC. After the evaluation, the function returns a doubleprecision number between –PI/2 and PI/2. If the number to be evaluated is larger than a double, use the atanl() function: long double atanl(long double x); This function takes a long double argument and returns a long double. 
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